What is the green vertical bar below the SMS sending time display?

Try to take off your mobile phone card before sending text messages. The message displayed at this time is that the transmission was unsuccessful.

The green one is a short message sent to Apple's mobile phone, which proves that the other party's mobile phone is Apple's. Of course, you have to make sure to open the read receipt first.

Then why are there blue signs? It's because blue is a voucher to send text messages to Android or other operating systems.